decoder: terminate decoder thread before MPD cleanup

When MPD exits, it should manually free all resources in use, to allow
easy memory leak debugging.  Make the decoder thread terminate during
that.

src/decoder_control.c

@@ -100,3 +100,10 @@ dc_seek(struct notify *notify, double where)
 
 	return true;
 }
+
+void
+dc_quit(struct notify *notify)
+{
+	dc.quit = true;
+	dc_command(notify, DECODE_COMMAND_STOP);
+}

src/decoder_control.h

@@ -49,6 +49,7 @@ struct decoder_control {
 
 	volatile enum decoder_state state;
 	volatile enum decoder_command command;
+	bool quit;
 	bool seek_error;
 	bool seekable;
 	volatile double seek_where;
@@ -122,4 +123,7 @@ dc_stop(struct notify *notify);
 bool
 dc_seek(struct notify *notify, double where);
 
+void
+dc_quit(struct notify *notify);
+
 #endif

src/decoder_thread.c

@@ -204,7 +204,7 @@ static void decoder_run(void)
 
 static void * decoder_task(G_GNUC_UNUSED void *arg)
 {
-	while (1) {
+	do {
 		assert(dc.state == DECODE_STATE_STOP ||
 		       dc.state == DECODE_STATE_ERROR);
 
@@ -226,7 +226,7 @@ static void * decoder_task(G_GNUC_UNUSED void *arg)
 			notify_wait(&dc.notify);
 			break;
 		}
-	}
+	} while (dc.command != DECODE_COMMAND_NONE || !dc.quit);
 
 	return NULL;
 }

src/player_thread.c

@@ -514,6 +514,7 @@ static void * player_task(G_GNUC_UNUSED void *arg)
 			break;
 
 		case PLAYER_COMMAND_EXIT:
+			dc_quit(&pc.notify);
 			closeAudioDevice();
 			player_command_finished();
 			pthread_exit(NULL);